TWI659671B - Driver circuit for driving light emitting device - Google Patents

Abstract

A light-emitting element driving circuit includes a power conversion circuit, an error amplifying circuit, a sampling and holding circuit, a load current generating circuit, and a feedforward capacitor. In the non-enabled phase, the feedback signal is electrically connected to the second reference voltage and disconnected from the load node through the sample-and-hold circuit. Thus, at the turning point of the non-enabled phase to the enable phase, the feedforward capacitor Sampling a sampling voltage. During the enabling phase, the feedback signal is disconnected from the second reference voltage and coupled to the load node through the sampling and holding circuit. The sampling voltage is maintained by the feedforward capacitor, so that the preset current rise time after the turning point is maintained. The feedback signal and the first reference voltage have a sufficiently large difference, so that the load current rises within a preset current rise time to reach the first current level.

Description

Light-emitting element driving circuit

The invention relates to a light-emitting element driving circuit, in particular to a load-transient response of a light-emitting element driving circuit which is improved by a sampling and maintaining circuit, so that the load current can be rapidly increased within a preset current rise time. A light-emitting element drive circuit that rises to reach a target current level.

Please refer to Figure 1 and Figure 2. FIG. 1 is a schematic diagram showing a light-emitting element driving circuit of the prior art. FIG. 2 is a waveform diagram of an operation signal of a light-emitting element driving circuit of the prior art.

In the light-emitting element driving circuit 100 of the prior art, when the light-emitting element driving circuit 100 is in a non-enable stage (that is, when the enable signal EN is at a low level), the level of the load current iLOAD is zero. At this time, previously, The feedback signal FB of the technology is at a very high voltage level (such as, but not limited to, 1.6V), and the corresponding error amplification signal COMP is, for example, zero. In the prior art, since the reference voltage VREF is set to a very low voltage level (such as but not limited to 0.2V). Therefore, as shown in FIG. 2, at a turning point Ts when the light-emitting element driving circuit 100 of the prior art transitions from the non-enabled phase to the enabled phase (meaning, when the enable signal EN changes from a low level to a high level). The feedback signal FB must be reduced from a very high voltage level (such as but not limited to 1.6V) to a very low voltage level (such as but not limited to 0.2V). Therefore, after the turning point Ts For a certain period of time T1, the error amplifier circuit 13 has not been switched, that is, its corresponding error amplifier signal COMP remains at zero. Therefore, the power conversion circuit 12 still cannot convert the power source VIN to provide the load current iLOAD, as shown in the figure. It is shown that, within time T1, the load current iLOAD cannot quickly rise to a target current level Ip. This is a major disadvantage of the prior art. During time T1, the load current iLOAD can only draw current from capacitor C2, however, such current level is still very low (as shown in the waveform diagram of load current Iload during time T1 shown in FIG. 2).

In addition, in the prior art, the load current iLOAD is related to the level of the feedback signal FB. Therefore, another major disadvantage of the prior art is that when the feedback signal FB drops below the reference voltage VREF (for example but not limited to 0.2V) When the level is still low, the feedback signal FB may be as low as, for example, but not limited to, 0.1V due to the overshoot effect. Since the load current iLOAD is related to the level of the feedback signal FB, the feedback signal FB is too low. The level will also cause the load current iLOAD to not reach its target current level Ip quickly, where the target current level Ip is, for example, the load current level corresponding to the feedback signal FB of 0.2V.

The present invention is directed to the above-mentioned problem and proposes a light-emitting element driving circuit. The load-transient response of the light-emitting element driving circuit is improved by the sampling and maintaining circuit, so that the load current can be adjusted within a preset current rise time. Light-emitting element driving circuit rising rapidly to reach a target current level.

In one aspect, the present invention provides a light-emitting element driving circuit for providing a load current to a light-emitting element to drive the light-emitting element. The light-emitting element driving circuit includes a power conversion circuit for detecting an error according to an error. Amplifying a signal, converting an input voltage to generate an output voltage at an output terminal and providing the load current to the light emitting element, the light emitting element is coupled between the output terminal and a load node; an error amplifying circuit, according to a first A difference between a reference voltage and a feedback signal generates the error amplification signal; a sampling and maintaining circuit is coupled between the feedback signal and the load node; a load current generating circuit, with the sampling and maintaining circuit and the light emitting The components are commonly coupled to the load node. The load current generating circuit is used to determine a first current level of the load current during the uniform energy phase, and is used to determine a second of the load current during a non-enabled phase. Current level; and a feed-forward capacitor, coupled between the output and the feedback signal; where, when When the light-emitting element driving circuit is in the non-enabled stage, the feedback signal is electrically connected to a second reference voltage with each other through the sampling and maintaining circuit, and the feedback signal is disconnected from the load node through the sampling and maintaining circuit. Therefore, when the non-enabling phase is turned into a turning point of the enabling phase, the feedforward capacitor samples a sampling voltage; wherein when the light-emitting element driving circuit is in the enabling phase, the feedback signal is maintained through the sampling. The circuit and the second reference voltage are disconnected from each other, and the feedback signal is coupled to the load node with each other through the sampling and maintaining circuit, wherein the sampling voltage is maintained by the feedforward capacitor so that after the turning point Within a preset current rise time, the feedback signal and the first reference voltage have a sufficiently large difference, so that the load current rises within the preset current rise time to reach the first current level.

In a preferred embodiment, the level of the second reference voltage is smaller than the level of the first reference voltage.

In a preferred embodiment, the level of the second reference voltage is equal to the level of the first reference voltage.

In a preferred embodiment, during the enabling phase, the load current generating circuit determines the first current level according to the voltage of the load node.

In a preferred embodiment, the first current level is related to the first reference voltage.

In a preferred embodiment, the load current generating circuit includes a voltage-controlled current source for adjusting the load current according to the voltage of the load node.

In a preferred embodiment, the sample-and-hold circuit includes: a resistor; a first switch coupled with the resistor in series between the load node and the feedback signal; and a second switch coupled Between the feedback signal and the second reference voltage; wherein when the light-emitting element driving circuit is in the non-enabled stage, the first switch is controlled to be non-conducting, and the second switch is controlled to be conducting, whereby the feedback The signal is electrically connected to the second reference voltage with each other through the sampling and maintaining circuit, and the feedback signal is disconnected from the load node, and the first switch is controlled to be turned on when the light-emitting element driving circuit is in the enabling stage. And the second switch is controlled to be non-conducting, whereby the feedback signal and the second reference voltage are disconnected from each other, and the feedback signal and the load node are coupled to each other.

In a preferred embodiment, the feed-forward capacitor provides a feed-forward function when the light-emitting element driving circuit is in the enabling stage, whereby the light-emitting element driving circuit operates in a stable state. And the bandwidth of the light-emitting element driving circuit is higher than a preset frequency.

In a preferred embodiment, the preset current rise time is related to the product of the resistance value of the resistor and the capacitance value of the feedforward capacitor.

In a preferred embodiment, the preset current rise time is less than 1 microsecond (μs).

In a preferred embodiment, the power conversion circuit includes a linear regulator or a switching power supply.

In a preferred embodiment, the second current level is zero.

In a preferred embodiment, the sufficiently large difference is smaller than a preset upper limit of the voltage difference, so that the load current rises within the preset current rise time to reach the first current level.

Detailed descriptions will be provided below through specific embodiments to make it easier to understand the purpose, technical content, features and effects of the present invention.

The drawings in the present invention are schematic, and are mainly intended to represent the coupling relationship between various circuits and the relationship between signal waveforms. As for the circuits, signal waveforms and frequencies, they are not drawn to scale.

Please refer to Figures 3 and 4. FIG. 3 is a block diagram illustrating an embodiment of a light-emitting element driving circuit according to the present invention. FIG. 4 shows an embodiment of a load current generating circuit according to the present invention.

As shown in FIG. 3, the light-emitting element driving circuit 200 of the present invention is used to provide a load current iLOAD to a light-emitting element LD to drive the light-emitting element LD to emit light. The light-emitting element LD may be, for example, but not limited to, a laser. Light-emitting diodes. Such high-energy light-emitting elements require extremely high drive currents. Generally, pulse-type currents are used to avoid problems such as overheating. Therefore, the light-emitting element driving circuit 200 needs to have a short preset current rise time. Within (for example, but not limited to 1 microsecond), the load current iLOAD is controlled to rise rapidly to reach the target current level (for example but not limited to 6A).

As shown in the figure, in one embodiment, the light-emitting element driving circuit 200 of the present invention may include: a power conversion circuit 12, an error amplifier circuit 13, a sample-and-hold circuit 15, a load current generating circuit 14, and a feedforward Capacitance (feed-forward capacitor) C1.

In one embodiment, the power conversion circuit 12 is used to convert the input voltage VIN to generate an output voltage VOUT at the output terminal OUT according to an error amplifying signal COMP, and provides a load current iLOAD to the light-emitting element LD. As shown in FIG. 3, the light-emitting element LD is coupled between the output voltage VOUT and a load node NLD. In one embodiment, the current inflow terminal of the light emitting element LD is coupled to the output voltage VOUT, and the current outflow terminal thereof is coupled to the load node NLD.

In an embodiment, as shown in FIG. 9A, the power conversion circuit may be, for example, but not limited to, a linear regulator, which is used to amplify the signal COMP according to the error, and convert the input voltage VIN to generate an output in a linear power conversion manner, for example. The voltage VOUT is at the output terminal OUT and provides a load current iLOAD to the light-emitting element LD. In another embodiment, as shown in FIG. 9B, the power conversion circuit may be, for example, but not limited to, a switching power supply for amplifying the signal COMP according to the error, and for example, switching the input voltage VIN by the switching power conversion method An output voltage VOUT is generated at the output terminal OUT and a load current iLOAD is provided to the light-emitting element LD.

Please continue to refer to FIG. 3. The error amplifier circuit 13 generates an error amplifier signal COMP according to a difference between a first reference voltage VREF_b and a feedback signal FB. In one embodiment, the error amplification signal COMP = a * (the first reference voltage VREF_b-the feedback signal FB). Here, a represents the amplification factor of the error amplifier circuit 13. It should be noted that the positive and negative terminals of the error amplifier circuit 13 as shown in the figure are used for illustration rather than limitation. Similarly, the positive and negative directions of the error amplifier signal COMP are the same. Under the teachings of the present invention, those skilled in the art When its configuration can be changed and implemented in different positive and negative signal directions.

The sample-and-hold circuit 15 is coupled between the feedback signal FB and the load node NLD (about how the present invention uses the sample-and-hold circuit 15 to improve the load-transient response of the light-emitting element drive circuits 200 and 300, thereby enabling The characteristics and details of the load current iLOAD rise rapidly within a preset current rise time to reach the target current level, which will be described later).

The feedforward capacitor C1 is coupled between the output terminal OUT and the feedback signal FB. The feedforward capacitor C1 has a voltage across VC1, as shown in Figure 3.

The load current generating circuit 14 is coupled to the sample and hold circuit 15 and the light emitting element LD to a load node NLD. The load current generating circuit 14 is used to determine a first current level of the load current iLOAD at a uniform energy stage (refer to the enabling signal EN in FIG. 3 and the waveform diagram of the enabling signal EN in FIG. 6), and is used for In a non-enable phase (refer to the enable signal EN in FIG. 3 and the waveform diagram of the enable signal EN in FIG. 6), a second current level of the load current iLOAD is determined. In an embodiment, the first current level Ip is, for example, but not limited to, the aforementioned 6A, and the second current level, such as, but not limited to, the current level 0, as shown in FIG. 6.

In one embodiment, the load current generating circuit 14 determines the first current level Ip according to the voltage of the load node NLD. In one embodiment, the first current level Ip is related to the first reference voltage VREF_b. For example, as shown in Figures 3 and 4, when VREF_b is set to 0.2V and in the steady state at the enable stage, the level of the feedback signal FB (that is, the voltage level of the load node NLD) is also roughly It is equal to 0.2V. In an embodiment, when the level of the feedback signal FB is 0.2V, the first current level Ip may correspond to 6A.

Please refer to Figure 4. In an embodiment, the load current generating circuit 14 may include, for example, but not limited to, a voltage-controlled current source 141. As shown in FIG. 4, the voltage-controlled current source 141 is controlled by the enable signal EN and adjusts the load current iLOAD according to the voltage of the load node NLD. In an embodiment, the load current iLOAD is, for example, but not limited to, the voltage level of the load node NLD (that is, the level of the feedback signal FB during the enabling phase).

Please refer to Figure 5A, Figure 5B and Figure 6. FIG. 5A illustrates a specific embodiment when the light-emitting element driving circuit of the present invention is in a non-enabled stage. FIG. 5B illustrates a specific embodiment when the light-emitting element driving circuit of the present invention is in an enabling stage. FIG. 6 shows a waveform diagram of an operation signal of the light-emitting element driving circuit of the present invention corresponding to FIGS. 5A-5B.

As shown in FIGS. 5A and 5B, in an embodiment, the sample-and-hold circuit 15 may include, for example, but not limited to, a resistor R1, a first switch S1, and a second switch S2. The first switch S1 and the resistor R1 are coupled in series with each other between the load node NLD and the feedback signal FB. The second switch S2 is coupled between the feedback signal FB and the second reference voltage VREF_a. It should be noted that the sequence of the first switch S1 and the resistor R1 in series with each other is not limited. In an embodiment, the sequence of the first switch S1 and the resistor R1 in series with each other may be as shown in FIGS. 5A and 5B.

The following describes how the present invention improves the load-transient response of the light-emitting element driving circuit 200 through the sampling and maintaining circuit 15 so that the load current iLOAD rises rapidly within a preset current rise time to reach the target current level. Accurate features and details.

As shown in FIG. 5A, in an embodiment, when the light-emitting element driving circuit 200 is in a non-enabled state, the first switch S1 is controlled by the enabling signal EN and controlled to be non-conductive by the enabling signal EN, and the first The two switches S2 are controlled by, for example, but not limited to, an inversion enabling signal ENb and controlled to be turned on by the inversion enabling signal ENb, whereby the feedback signal FB is electrically connected to the second reference voltage VREF_a through the sampling and maintaining circuit 15. , And the feedback signal FB is disconnected from the load node NLD through the sample and hold circuit. As a result, when the light-emitting element driving circuit 200 transitions from the non-enabled stage to the enabled stage Ts (see the waveform diagram of the enabling signal EN in FIG. 6), the feedforward capacitor C1 samples a sampling voltage Vsmpl (see Waveform diagram of output voltage VOUT and feedback signal FB in Fig. 6). It is worth noting that the sampling voltage “Vsmpl” mentioned here refers to the voltage level of the cross-voltage VC1 of the feedforward capacitor C1 in the non-enabled stage.

As shown in FIG. 5B, in an embodiment, when the light-emitting element driving circuit 200 is in an enabling stage, the first switch S1 is controlled by the enabling signal EN and controlled to be turned on by the enabling signal EN, and the second switch S2 is controlled by an inversion enabling signal ENb and is controlled to be non-conducting by the inversion enabling signal ENb, whereby the feedback signal FB is disconnected from the second reference voltage VREF_a through the sample and hold circuit 15 and the feedback signal FB is coupled to the load node NLD via the sample and hold circuit 15.

Therefore, when the light-emitting element driving circuit 200 is in the enable stage, the sampling voltage Vsmpl is maintained by the feedforward capacitor C1 (that is, Vhold in FIG. 6 is approximately equal to Vsmpl), so that the preset current rise time after the turning point Ts Within Tr (refer to the waveform diagram of the feedback signal FB in FIG. 6), the feedback signal FB and the first reference voltage VREF_b have a sufficiently large difference, so that the load current iLOAD rises within the preset current rise time Tr to reach the first A current level Ip.

In one embodiment, the feedforward capacitor C1 provides a feed-forward function when the light-emitting element driving circuit 200 is in the enable stage, and is used as loop compensation and bandwidth adjustment of the driving circuit 200 to drive the light-emitting element. The circuit 200 can be operated in a stable state, and the frequency bandwidth of the light-emitting element driving circuit 200 can be higher than a preset frequency. It is worth noting that in this embodiment, the feedforward capacitor C1 of the present invention has both the aforementioned feedforward function and the function of sampling and maintaining, while taking into account the loop stability, frequency bandwidth, and current rising speed without increasing cost.

In an embodiment, the product of the resistance value of the resistor R1 and the capacitance value of the feedforward capacitor C1 determines a time constant of a load-transient response of the light-emitting element driving circuit 200, wherein the preset current rise time is Tr is related to the time constant. In other words, the preset current rise time Tr is related to the product of the resistance value of the resistor R1 and the capacitance value of the feedforward capacitor C1.

In one embodiment, the preset current rise time Tr may be, for example, but not limited to, less than 1 microsecond (μs). It is worth noting that, in the present invention, since the value of the preset current rise time Tr is small, under the same enable signal operation, compared with the previous case, the load current iLOAD of the present invention is at the enable stage The pulse width Tw is significantly higher than the pulse width of the load current in the previous case (as shown in Figures 6 and 8). In other words, the light-emitting element driving circuit of the present invention can effectively improve the brightness of the light-emitting element LD or other Parameter performance.

In addition, in the light-emitting element driving circuit 200 of this embodiment, when the light-emitting element driving circuit 200 is in the enable stage (that is, when the enable signal EN is at a high level), since the present embodiment includes a sample-and-hold circuit 15, The control details described above cause the feedback signal FB to be disconnected from the second reference voltage VREF_a via the sample and hold circuit 15. In this way, within the preset current rise time Tr, the level of the feedback signal FB will gradually rise to a first reference voltage VREF_b from a voltage level slightly lower than the second reference voltage VREF_a through the trend of feedback control. . That is to say, in one embodiment, when the light-emitting element driving circuit 200 is in a steady state in the enabling stage, the level of the feedback signal FB is substantially equal to the first reference voltage VREF_b.

It should be noted that, in the embodiment of FIG. 6, the level of the second reference voltage VREF_a is smaller than the level of the first reference voltage VREF_b. However, the spirit of the present invention is not limited to this. The level of the second reference voltage VREF_a may be equal to, or slightly greater than, the level of the first reference voltage VREF_b. The embodiment of the second reference voltage VREF_a is equal to the level of the first reference voltage VREF_b. .

In this embodiment, when the light-emitting element driving circuit 200 is in the enabling stage (that is, when the enabling signal EN is at a high level), since the load current iLOAD is related to the feedback signal FB (when the steady state in the enabling stage, it is The level is substantially equal to the first reference voltage VREF_b), and because the time required for the level of the feedback signal FB to rise from the second reference voltage VREF_a to the first reference voltage VREF_b is very short, compared with the prior art, this implementation For example, the load current generating circuit 14 can quickly determine the first current level Ip of the load current iLOAD according to the voltage of the load node NLD (that is, the level of the feedback signal FB). The preset current rise time Tr can rise rapidly to reach the target current level Ip. From a viewpoint, the relationship between the second reference voltage VREF_a and the first reference voltage VREF_b (that is, the magnitude and difference) can be appropriately selected, so that when the light-emitting element driving circuit is switched to the enabling stage, the feedforward The capacitor maintains the sampling voltage, and within a preset current rise time after the turning point, the sufficiently large difference between the aforementioned feedback signal and the first reference voltage is smaller than a preset upper limit of the voltage difference, so that The load current generating circuit determines the first current level within a preset current rise time.

Please refer to Figure 7A, Figure 7B and Figure 8. FIG. 7A illustrates another specific embodiment when the light-emitting element driving circuit of the present invention is in a non-enabled stage. FIG. 7B illustrates another specific embodiment when the light-emitting element driving circuit of the present invention is in an enabling stage. FIG. 8 shows waveform diagrams of operation signals of the light-emitting element driving circuit of the present invention corresponding to FIGS. 7A-7B.

The light-emitting element driving circuit 300 shown in Figs. 7A-7B is substantially similar to the light-emitting element driving circuit 200 shown in Figs. 5A-5B. The difference lies in the implementation of the light-emitting element driving circuit 300 shown in Figs. 7A-7B. In an example, the level of the second reference voltage VREF_a is equal to the level of the first reference voltage VREF_b. In the embodiment of the light-emitting element driving circuit 300 shown in FIGS. 7A-7B, for example, but not limited to, the second reference voltage VREF_a may be directly coupled to the first reference voltage VREF_b.

In this way, as shown in FIG. 7A, in an embodiment, when the light-emitting element driving circuit 300 is in a non-enabled state, the first switch S1 is controlled by the enable signal EN and controlled by the enable signal EN to be inactive. Is turned on, and the second switch S2 is controlled by an inversion enabling signal ENb and controlled to be turned on by the inversion enabling signal ENb, whereby the feedback signal FB is electrically connected to the first reference voltage VREF_b through the sampling and maintaining circuit 15 , And the feedback signal FB is disconnected from the load node NLD through the sample and hold circuit. As a result, when the light-emitting element driving circuit 300 transitions from the non-enabled phase to the enabled phase Ts (see the waveform diagram of the enabling signal EN in FIG. 8), the feedforward capacitor C1 samples a sampling voltage Vsmpl (see Waveform diagram of output voltage VOUT and feedback signal FB in Fig. 8). It is worth noting that the “Vsmpl” of the sampling voltage Vsmpl mentioned here refers to the voltage level of the cross-voltage VC1 of the feedforward capacitor C1 in the non-enabled stage.

As shown in FIG. 7B, in an embodiment, when the light-emitting element driving circuit 200 is in the enabling stage, the first switch S1 is controlled by the enabling signal EN and controlled to be turned on by the enabling signal EN, and the second switch S2 is controlled by an inversion enabling signal ENb and is controlled to be non-conducting by the inversion enabling signal ENb, whereby the feedback signal FB is disconnected from the first reference voltage VREF_b to each other through the sampling and holding circuit 15 and the feedback signal FB is coupled to the load node NLD via the sample and hold circuit 15.

Therefore, when the light-emitting element driving circuit 300 is in the enable stage, the sampling voltage Vsmpl is maintained by the feedforward capacitor C1 (that is, Vhold in FIG. 8 is approximately equal to Vsmpl), so that the preset current rise time after the turning point Ts Within Tr (refer to the waveform diagram of the feedback signal FB in Fig. 8), the feedback signal FB and the first reference voltage VREF_b have a sufficiently large difference, so that the load current iLOAD rises within a preset current rise time Tr to reach First current level Ip.

Compared with the prior art, the load current iLOAD of the light-emitting element driving circuit 300 in this embodiment can rise rapidly within a preset current rise time Tr to reach the target current level Ip. The following uses Figures 6 and 8 to illustrate the differences between the present invention and the prior art: That is, the present invention can improve the load-transient response of the light-emitting element driving circuit 200, so that the load current iLOAD is at a preset current. Rise quickly during the rise time to reach the target current level.

In the light-emitting element driving circuits 200 and 300 in this embodiment, when the light-emitting element driving circuit 200 is in a non-enabled stage (meaning that the enabling signal EN is at a low level), the present invention includes a sampling and holding circuit 15 as above. The control details make the feedback signal FB and the second reference voltage VREF_a electrically connected to each other via the sample and hold circuit 15, wherein the level of the second reference voltage VREF_a is lower than (FIG. 6) or equal to (FIG. 8) the A level of a reference voltage VREF_b. In this way, compared with the feedback signal FB of the prior art at a high voltage level (for example, but not limited to 1.6V), the feedback signal FB of the present invention is coupled when it is not enabled. To the second reference voltage VREF_a or the first reference voltage VREF_b, that is, slightly lower than or equal to the target value (the first reference voltage VREF_b) to be achieved in the enabling phase. This advantage is that, as shown in FIG. 6 or FIG. 8, when the light-emitting element driving circuit 200 or 300 of this embodiment is switched to the enable stage at a non-enable stage (that is, the enable signal EN is high on time) At a turning point Ts, the feedback signal FB does not have to be reduced from a very high voltage level to a very low voltage level. This can effectively shorten the response time of the feedback signal FB and thereby increase the current rising speed.

In addition, because the output voltage VOUT decreases due to the load current iLOAD, the function of sampling and maintaining the feedforward capacitor C1 (that is, Vsmpl and Vhold in Figure 6 or Figure 8), after the turning point Ts For a period of time (e.g., the previous stage of the preset current rise time Tr in FIG. 6 or FIG. 8), the level of the feedback signal FB decreases substantially synchronously from the second reference voltage VREF_a and the output voltage VOUT (due to The feed-forward capacitor C1 across the voltage VC1 in the previous section of the preset current rise time Tr in FIG. 8 is still substantially maintained at the voltage level Vhold sampled at the turning point, which is approximately equal to Vsmpl) to a value slightly lower than the second reference. The voltage level of the voltage VREF_a (below the first reference voltage VREF_b). At this time, the corresponding error amplification signal COMP will respond quickly or change state (for example, in Figure 6, the original high level is quickly reduced to a low level). Therefore, the power conversion circuit 12 can quickly provide the load current iLOAD, and therefore, within the preset current rise time Tr, the load current iLOAD can quickly rise to the target current level Ip.

Please refer to FIGS. 10A to 10B, which show measurement waveform diagrams of the load-transient response of the light-emitting element driving circuit of the present invention. As shown in FIG. 10A, the load current iLOAD of the light-emitting element driving circuit in this embodiment can quickly rise to reach the target current level within a preset current rise time Tr. FIG. 10B is an enlarged schematic diagram of FIG. 10A. As shown in FIG. 10B, it can be clearly seen that the load current iLOAD of the light-emitting element driving circuit of this embodiment can quickly rise to reach the target within a preset current rise time. Current level.

The present invention has been described above with reference to the preferred embodiments, but the above is only for making those skilled in the art easily understand the content of the present invention, and is not intended to limit the scope of rights of the present invention. In the same spirit of the invention, those skilled in the art can think of various equivalent changes. For example, between the directly connected circuit elements, circuit elements such as switches or resistors that do not affect the main function of the circuit can be inserted. For another example, the aforementioned first switch S1 is controlled by the enabling signal EN, and the second switch S2 is controlled by the inverting enabling signal ENb. This is merely an example and not a limitation. When the first switch S1 and the second switch S2 are Different types of transistors can also be controlled by the enable signal EN. All these can be deduced by analogy according to the teachings of the present invention. In addition, each of the embodiments described is not limited to separate applications, and can also be applied in combination, such as, but not limited to, combining the two embodiments, or substituting a local circuit of one embodiment for a corresponding circuit of another embodiment. Therefore, the scope of the invention should cover the above and all other equivalent variations. In addition, any embodiment of the present invention does not have to achieve all the objectives or advantages. Therefore, any one of the scope of the claimed patent should not be limited to this.

100‧‧‧ conventional light-emitting element driving circuit

VREF‧‧‧Reference voltage

T1‧‧‧ Learned time

200, 300‧‧‧ light-emitting element driving circuit

12‧‧‧Power Conversion Circuit

13‧‧‧Error amplification circuit

14‧‧‧Load current generating circuit

141‧‧‧Voltage-controlled current source

15‧‧‧Sampling and holding circuit

C1‧‧‧Feed-forward capacitor

COMP‧‧‧Error amplification signal

EN‧‧‧Enable signal

ENb‧‧‧ Reverse Phase Enable Signal

FB‧‧‧ feedback signal

iLOAD‧‧‧Load current

Ip‧‧‧first current level

LD‧‧‧Light-emitting element

NLD‧‧‧Load Node

OUT‧‧‧output

R1‧‧‧ resistance

S1‧‧‧First switch

S2‧‧‧Second switch

Tf‧‧‧Preset current fall time

Tr‧‧‧Preset current rise time

Ts‧‧‧ turning point

Tw‧‧‧pulse width

ΔV‧‧‧Voltage difference

VC1‧‧‧ Crossover voltage of feedforward capacitor

VOUT‧‧‧Output voltage

Vsmpl‧‧‧Sampling voltage

Vhold‧‧‧Voltage Level

VREF_a‧‧‧second reference voltage

VREF_b‧‧‧first reference voltage

FIG. 1 is a schematic diagram showing a light-emitting element driving circuit of the prior art. FIG. 2 is a schematic diagram showing an operation signal waveform of a light-emitting element driving circuit of the prior art. FIG. 3 is a block diagram illustrating an embodiment of a light-emitting element driving circuit according to the present invention. FIG. 4 is a schematic diagram of an embodiment of a load current generating circuit according to the present invention. FIG. 5A is a schematic diagram of a specific embodiment when the light-emitting element driving circuit of the present invention is in a non-enabled stage. FIG. 5B is a schematic diagram of a specific embodiment when the light-emitting element driving circuit of the present invention is in an enabling stage. FIG. 6 is a schematic diagram of operation signal waveforms of the light-emitting element driving circuit of the present invention corresponding to FIGS. 5A-5B. FIG. 7A shows a schematic diagram of another specific embodiment when the light-emitting element driving circuit of the present invention is in a non-enabled stage. FIG. 7B is a schematic diagram of another specific embodiment when the light-emitting element driving circuit of the present invention is in an enabling stage. FIG. 8 is a schematic diagram of operation signal waveforms of the light-emitting element driving circuit of the present invention corresponding to FIGS. 7A-7B. FIG. 9A illustrates a schematic diagram of an embodiment of a power conversion circuit according to the present invention. FIG. 9B illustrates a schematic diagram of another embodiment of the power conversion circuit of the present invention. 10A to 10B are diagrams showing load-transient response measurement waveform diagrams of the light-emitting element driving circuit of the present invention.

Claims (13)

A light-emitting element driving circuit for providing a load current to a light-emitting element to drive the light-emitting element. The light-emitting element driving circuit includes: a power conversion circuit for amplifying a signal according to an error and converting an input voltage to generate a An output voltage is provided at an output terminal and the load current is provided to the light emitting element, the light emitting element is coupled between the output terminal and a load node; an error amplifying circuit, according to a difference between a first reference voltage and a feedback signal Value, the error amplification signal is generated; a sampling and maintaining circuit is coupled between the feedback signal and the load node; a load current generating circuit is coupled to the load node with the sampling and maintaining circuit and the light emitting element, the The load current generating circuit is used to determine a first current level of the load current in a uniform energy phase, and is used to determine a second current level of the load current in a non-enabled phase; and a feedforward capacitor ( feed-forward capacitor), coupled between the output terminal and the feedback signal; wherein when the light-emitting element driving circuit is in the During the enabling phase, the feedback signal is electrically connected to a second reference voltage with each other through the sampling and holding circuit, and the feedback signal is disconnected from the load node with each other through the sampling and holding circuit, thereby enabling the non-enabled When the phase transitions to a turning point in the enabling phase, the feedforward capacitor samples a sampling voltage; wherein, when the light-emitting element driving circuit is in the enabling phase, the feedback signal passes through the sampling and maintaining circuit to communicate with the second The reference voltages are disconnected from each other, and the feedback signal is coupled to the load node with each other via the sampling and holding circuit, wherein the sampling voltage is maintained by the feedforward capacitor, so that a preset current after the turning point is increased Within time, the feedback signal and the first reference voltage have a sufficiently large difference, so that the load current rises within the preset current rise time to reach the first current level. . The light-emitting element driving circuit according to item 1 of the application, wherein a level of the second reference voltage is smaller than a level of the first reference voltage. The light-emitting element driving circuit according to item 1 of the scope of patent application, wherein the level of the second reference voltage is equal to the level of the first reference voltage. According to the light-emitting element driving circuit described in the first item of the patent application scope, in the enabling stage, the load current generating circuit determines the first current level according to the voltage of the load node. The light-emitting element driving circuit according to item 4 of the patent application, wherein the first current level is related to the first reference voltage. The light-emitting element driving circuit according to item 4 of the scope of the patent application, wherein the load current generating circuit includes a voltage-controlled current source for adjusting the load current according to the voltage of the load node. The light-emitting element driving circuit as described in any one of claims 1 to 6, wherein the sampling and holding circuit includes: a resistor; a first switch coupled with the resistor in series with each other between the load node and the load node; Between the feedback signal; and a second switch coupled between the feedback signal and the second reference voltage; wherein when the light-emitting element driving circuit is in the non-enabled stage, the first switch is controlled to be non-conducting, and The second switch is controlled to be on, whereby the feedback signal and the second reference voltage are electrically connected to each other through the sampling and holding circuit, and the feedback signal and the load node are disconnected from each other, and when the light-emitting element driving circuit is in During the enabling phase, the first switch is controlled to be conductive and the second switch is controlled to be non-conductive, whereby the feedback signal and the second reference voltage are disconnected from each other, and the feedback signal and the load node are coupled to each other Pick up. The light-emitting element driving circuit according to item 1 of the patent application scope, wherein the feed-forward capacitor provides a feed-forward function when the light-emitting element driving circuit is in the enabling stage, thereby the light-emitting element driving circuit It operates in a stable state, and the bandwidth of the light-emitting element driving circuit is higher than a preset frequency. The light-emitting element driving circuit according to item 7 of the scope of the patent application, wherein the preset current rise time is related to a product of a resistance value of the resistor and a capacitance value of the feedforward capacitor. The light-emitting element driving circuit according to item 1 of the application, wherein the preset current rise time is less than 1 microsecond (μs). The light-emitting element driving circuit according to item 1 of the patent application scope, wherein the power conversion circuit includes a linear regulator or a switching power supply. The light-emitting element driving circuit according to item 1 of the scope of patent application, wherein the second current level is zero. The light-emitting element driving circuit according to item 1 of the scope of patent application, wherein the sufficiently large difference is smaller than a preset upper limit of the voltage difference, so that the load current rises within the preset current rise time to reach the first Current level.